1. Field of the Invention
The present invention relates to a method of forming a transparent color image using electro-photography.
2. Description of the Related Art
Conventionally, an image is commonly projected by using an over-head projector (hereinafter referred to OHP), which image has been obtained by forming a monochrome image on a transparent film (transparent base film) made of polyester, etc., by an electro-photographic apparatus.
However, when a full-color image is formed on a transparent film by dry developing and projected by the OHP, the thus-projected image becomes grayish and exhibits a very narrow range of color reproducibility.
This is because light is irregularly reflected by a roughness of the toner-image surface which has been caused during image-forming on the transparent base film. In other words, toner provided on the smooth transparent film does not satisfactorily melt or flow due to heating applied at the time of fixation. Thus, a particle form of the toner is maintained such that incident light is irregularly reflected thereby, and for instance, a shadow occurs on the screen, resulting in a deteriorated image. In particular, since the number of toner particles is small in half-tone portions having low image densities, light absorption by coloring agent or pigment included in the toner decreases to a level similar to that by the irregular reflection, therefore the color reproduction of the half-tone portions becomes grayish.
To solve the foregoing problems, Japanese Patent Laid-Open No. 2-263642 and U.S. Pat. No. 5,229,188 disclose methods of smoothing the surfaces of transparent image supporting members (transparent base films) by coating a resin miscible with toner. The transparency of the toner images is thereby improved and excellent projected images are achieved.
Meanwhile, among the color images, such images that have the highlighted portions require further transparency in the toner image so as to achieve excellent color reproducibility of the projected images.